Insights into mechanical compression and the enhancement in performance by Mg(OH)2 coating in flexible dye sensitized solar cells

Abstract

The engineering of flexible dye sensitized solar cells (DSCs) by mechanical compression is one of the methods that allow low temperature processing of these devices. However, suppressing the high temperature sintering process also significantly reduces the performance of the cells. In our previous work [J. Phys. Chem. C, 116 (2012) 1211], we have attempted to improve flexible DSC performance by coating the porous TiO 2 photoanode with an electrodeposited Mg(OH) 2 layer. In that work, we have 10 obtained one of the largest photovoltage reported to date in flexible DSCs (847 mV). In order to gain more insights into the reasons for both poorer performance of compressed cells and the origin of the voltage enhancement achieved by the Mg(OH) 2 coating, here we present an in-depth study by means of electrochemical impedance spectroscopy, Mott-Schottky plots analysis and open-circuit voltage decays. The existence of a shunt resistance in the mechanically compressed cells is revealed, causing an 15 additional drawback to the poor inter-particle necking. By introducing the Mg(OH) 2 coating the recombination in the cell becomes significantly reduced, being the key reason which is responsible for the higher photovoltage. Additionally, the coating and the compression cause modifications in the surface states and in the nature of the interfaces with the electrolyte. This induces TiO 2 conduction band displacements and shifts of the relative position of the modified states that influence the performance.

Electronic and optical properties of magnesium and calcium hydroxides: the role of covalency and many-body effects

“…For example, coating the TiO 2 nanoparticles with a metal oxide has enhanced the conversion efficiency of the cell. It was reported [13,14] that a coating of TiO 2 by Mg(OH) 2 improved the open-circuit voltage of a dyesensitized solar cell. Suppression of charge carrier recombination at the interface of the dye-sensitized solar cells has been reported [15] for Ca(OH) 2 .…”

“…Suppression of charge carrier recombination at the interface of the dye-sensitized solar cells has been reported [15] for Ca(OH) 2 . Mg(OH) 2 has been used as a buffer layer in CuInSe [16,17] cells and as a passivation layer in dyesensitized [13][14][15]18] composite solar cells.…”

Improving the Conversion Ratio of QDSCs via the Passivation Effects of NiS

“…In order to reduce carrier recombination, the passivation of the photoanode nanostructure with a wide band gap with other materials with a smaller band gap is a promising strategy. Two types of passivation layers have been reported through thin insulating passivation layers of metal oxides, such as ZrO 2 [19], Al 2 O 3 [20], HfO 2 [21], and SiO 2 [22,23]. The second one is through the sulfide semiconductor passivation layer, which increases the QD loading mass, reduces surface defects, and traps charge recombination.…”

Effect of Electrochemically Deposited MgO Coating on Printable Perovskite Solar Cell Performance

“…However, unevenness, surface defects and the presence of pin holes in this layer are often responsible for reducing the cell performance. Therefore, over the last years, many attempts have been made to enhance the overall cell performance of PSCs by retarding the back transfer of photo-generated electrons through the FTO/TiO 2 interface by surface modification of TiO 2 using insulating metal oxides [10][11][12] and hydroxides [13,14] or high band gap semiconductors [15,16] that form a blocking layer between the perovskite sensitizer and TiO 2 layer to block the back electron flow towards the HTM. For instance, TiO 2 modification with a monolayer of silane [17] and ZnO with 3-aminopropanioc acid self-assembled monolayer [18] have been found to enhance the device efficiency by retarding the back electron transfer processes of PSCs.…”